Channel 4 has pulled phone-ins from its coverage of the Cheltenham Festival after discovering a problem on its horse racing show The Morning Line.
John McCririck is part of Channel 4's Morning Line presenting team
About 100 people were charged for calling a competition after lines had closed, chief executive Andy Duncan told a House of Commons committee.
The mistake was discovered by auditors appointed to review Channel 4's live phone-ins following recent problems.
Mr Duncan said Channel 4 was contacting the callers to arrange refunds.
The error was apparently due to a computer glitch at phone service provider Eckoh.
The company also provides services to Richard and Judy, Saturday Kitchen and Ant and Dec's Saturday Night Takeaway - all of which are under investigation by phone line watchdog Icstis.
ITV denied David Gest was wrongly evicted from I'm a Celebrity...
Mr Duncan said if competitions returned to its horse racing coverage, Channel 4 would probably use "somebody else" to run them.
The latest phone-in problem came as ITV denied mistakes with vote-counting on reality show I'm a Celebrity... Get Me Out of Here.
The Sun newspaper claimed David Gest was wrongly evicted from last year's series after 30,000 text votes intended to save the star were not counted.
"This accusation is completely wrong," an ITV statement said. "On the night of David Gest's eviction, all votes were counted and verified."
Eckoh, which ran the voting lines, said it was seeking legal advice over the "maliciously fabricated" claims.
"Eckoh and its staff have been put under intense scrutiny in recent weeks and this cannot be allowed to continue," chief executive Nik Philpot said.
"On that basis we are taking legal advice and we will be reporting the matter to the police."
Icstis said it was looking into the claims, but has not launched a formal investigation.
Speaking to the House of Commons Culture, Media and Sport Committee, ITV executive chairman Michael Grade said he was "really surprised" at the Sun story.
Mr Grade also defended the use of interactive votes on ITV shows, and suggested viewers should develop a "sense of humour" over seemingly impossible questions.
One maths question on the late-night Make Your Play show proved so difficult that even an Oxford University maths professor was unable to solve it.
Grade insisted the question was a "schoolboy riddle" cast in the "great tradition of cryptic questions".
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He added that as long as the public enjoyed phone quizzes it was "perfectly proper to make a margin of profit" from them.
But Mr Grade admitted programme staff had not understood the importance of complying with phone-in regulations.
"In the excitement of a live gallery - which is a pretty fevered place on a big network show - I don't think the training and the importance of compliance has really sunk in," he said.
He also revealed the number of votes for Dancing on Ice had risen last week, suggesting public confidence had not been affected by the current problems.
The committee was told premium rate phone-ins were a vital part of programming.
Five chief executive Jane Lighting said telephone services were "due to deliver about £8m" to the channel in 2006.
"If you look at our children's programming, our entire production cost is around £6m, so it is an important contributor to our funding," she said.
Icstis is currently investigating three shows: Channel 4's Richard and Judy, the BBC's Saturday Kitchen and ITV's The X Factor.
Possible regulations breaches on ITV's Soapstar Superstar, Ant and Dec's Saturday Night Takeaway and I'm A Celebrity... Get Me Out Of Here! are also being looked into, but no formal investigations have been launched.